x is the number of your interface card. Add Value name Adaptive_ifs as type REG_DWORD and set it to 1. This will enable an adaptive algorithm, while 0 will disabled it. A value of 2 - 200 sets a predefined interframe gap, if you want to measure collisions at 20, 40, 60, ..... and pick one with a low collision rate and good performance.

If you have a different NIC, edit:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

and add Value name TcpWindowSize as type REG_DWORD and set it to 2920 (decimal).

Note: This tip is for 100MB EtherNet TCP/IP networks only. Using this parameter on a 10MB network, or on a WAN or FDDI, or Token Ring, or anything else, will impact performance.